1. Field of the Invention
The present invention relates to a substrate processing method and a substrate processing unit, and more particularly to a substrate processing method and a substrate processing unit which are used to carry out processing, such as cleaning or drying, a surface of a substrate, such as a semiconductor wafer, in a contactless manner.
2. Description of the Related Art
A two-fluid jet (2FJ) cleaning method is known as a cleaning method for cleaning a substrate surface in a contactless manner. This cleaning method involves jetting a high-speed gas containing fine liquid droplets (mist) from a two-fluid nozzle toward a substrate surface and causing the fine liquid droplets to collide against the substrate surface. The cleaning method utilizes a shock wave, generated by the collision of fine liquid droplets against the substrate surface, to remove (clean off) particles, etc. from the substrate surface.
A drying method using an IPA (isopropyl alcohol) vapor is known as a drying method for drying a substrate surface in a contactless manner. This drying method involves blowing a gas containing an IPA vapor from a fluid nozzle toward a gas-liquid interface on a substrate surface. The drying method evaporates and removes a liquid film from the substrate surface by utilizing the gradient of the surface tension of the liquid film present on the substrate surface and the promotion of evaporation of the liquid by the IPA vapor.
In the conventional two-fluid jet cleaning method, it is common practice to jet a mixed fluid from a two-fluid nozzle toward a substrate surface while moving the two-fluid nozzle, mounted at a front end of a swing arm, parallel to the substrate surface at a constant speed by swinging (rotating) the swing arm at a constant angular velocity. Therefore, as the two-fluid nozzle moves toward the periphery of the substrate, the amount of liquid droplets supplied per unit area of the substrate surface gradually decreases, and the density of liquid droplets colliding against the substrate surface decreases, leading to a decreases in the cleaning effect.
In the drying method using an IPA vapor, there are cases where the angular velocity of a swing arm is changed to change the movement speed of a fluid nozzle mounted at the front end of the swing arm. The degree of change of the movement speed of the fluid nozzle is in most cases determined empirically. This sometimes involves discontinuity in the movement speed of the fluid nozzle, which may result in uneven drying of a substrate surface.
In order to reduce variation in the cleaning effect in a substrate surface, a method has been proposed which involves gradually decreasing the movement speed of a fluid nozzle, such as a cleaning nozzle, as distance from the center of the substrate increases (see e.g., Japanese Patent Laid-Open Publication Nos. H11-47700, H11-307492 and 2005-93694).
The proposed method, however, does not take account of the relationship between factors such as processing time (throughput) and the movement speed of a fluid nozzle such as a cleaning nozzle. Thus, it is considered necessary to newly set the movement speed of a fluid nozzle such as a cleaning nozzle in order to shorten the cleaning or drying time and to thereby increase the throughput, for example.
The applicant has proposed a variety of two-fluid jet cleaning methods for cleaning a substrate surface after polishing efficiently with a mixture of a gas and a liquid jetted against the substrate surface, and a variety of drying methods for drying a substrate surface by using an IPA vapor (see e.g., International Publication No. 2007/108315 pamphlet and Japanese Patent Laid-Open Publication Nos. 2010-50436 and 2010-238850).